Pathobiology of Cancer
Cancer is characterized primarily by an increase in the number of abnormal cells derived from a given normal tissue, invasion of adjacent tissues by these abnormal cells, or lymphatic or blood-borne spread of malignant cells to regional lymph nodes and to distant sites (metastasis). Clinical data and molecular biologic studies indicate that cancer is a multistep process that begins with minor preneoplastic changes, which may under certain conditions progress to neoplasia. The neoplastic lesion may evolve clonally and develop an increasing capacity for invasion, growth, metastasis, and heterogeneity, especially under conditions in which the neoplastic cells escape the host's immune surveillance. Roitt, I., Brostoff, J and Kale, D., Immunology, 17.1-17.12 (3rd ed., Mosby, St. Louis, Mo., 1993).
There is an enormous variety of cancers which are described in detail in the medical literature. Examples include cancer of the lung, colon, rectum, pancreatic, prostate, breast, brain, and intestine. The incidence of cancer continues to climb as the general population ages, as new cancers develop, and as susceptible populations grow. A tremendous demand therefore exists for new methods and compositions that can be used to treat patients with cancer.
Solid Tumors
Over 85% of human cancers are solid tumors, including carcinomas, sarcomas and lymphomas. Jain, et al. Int J Pharm Pharm Sci, 2011, Vol 3, Suppl 5, 45-51. Solid tumors are abnormal masses of tissue that may, but usually do not contain cysts or liquid areas. Solid tumors may be benign (not cancer), or malignant (cancer). Different types of solid tumors are named for the type of cells that form them. Examples of types solid tumors include, but are not limited to malignant melanoma, adrenal carcinoma, breast carcinoma, renal cell cancer, carcinoma of the pancreas, non small-cell lung carcinoma (NSCLC) and carcinoma of unknown primary.
The effectiveness of cancer therapy in solid tumors depends on adequate delivery of the therapeutic agent to tumor cells. Inadequate delivery would result in residual tumor cells, which in turn would lead to regrowth of tumors and possibly development of resistant cells. In addition, the long-standing problem of chemotherapy is the lack of tumor-specific treatments. Cancer chemotherapeutic agents are often administered systemically. Following a systemic administration, drug delivery to cells in solid tumors involves three processes, i.e., transport within a vessel (e.g., blood circulation), transport across vasculature walls into surrounding tissues, and transport through interstitial space within a tumor. These processes are determined by the physicochemical properties of a drug or particle (e.g., molecular or particle size, diffusivity, drug binding to cellular macromolecules) and the biologic properties of a tumor (e.g., tumor vasculature, extracellular matrix components, interstitial fluid pressure (IFP), tumor cell density, tissue structure and composition). Cancer drug delivery is no longer simply wrapping the drug in new formulations for different routes of delivery. Nanotechnology, polymer chemistry and electronic engineering technologies are being brought for developing novel methods of drug delivery. Various stages of tumor development can be explained as follows:
a) Tumor evolution commences when a cell within a normal population sustains a genetic mutation that expands its tendency to proliferate when it would normally rest.
b) Genetically altered cells and their offspring continue to appear normal, but they reproduce excessively and lead to a condition termed to as hyperplasia. After some time (months or years) one in a million of these cells sustain additional mutation with subsequent loss of control of cell growth.
c) The offspring of these cells not only proliferate excessively but also appear abnormal in shape and in orientation. The tissue is now said to exhibit a condition termed to as dysplasia. After some time, a further mutation that alters cell behavior results.
d) The influenced and genetically altered cells turn still more abnormal in growth and appearance. If the tumor mass does not invade through any boundaries between tissues, it is termed as an in situ tumor. This tumor may stay contained indefinitely, however, some cells may acquire additional mutations.
e) A malignant or invasive tumor results if the genetic changes allow the tumor mass to initiate invading underlying tissue and to cast off cells into the blood or lymph. The defector cells may install new tumors loci (metastases) throughout the body.
Metastases represent the end products of a multistep cell-biological process termed the invasion-metastasis cascade, which involves dissemination of cancer cells to anatomically distant organ sites and their subsequent adaptation to foreign tissue microenvironments. Each of these events is driven by the acquisition of genetic and/or epigenetic alterations within tumor cells and the co-option of nonneoplastic stromal cells, which together endow incipient metastatic cells with traits needed to generate macroscopic metastases. Volastyan, S., et al., Cell, 2011, vol. 147, 275-292.
Whereas surgical resection and adjuvant therapy can cure well-confined primary tumors, metastatic disease is largely incurable because of its systemic nature and the resistance of disseminated tumor cells to existing therapeutic agents. This explains why >90% of mortality from cancer is attributable to metastases, not the primary tumors from which these malignant lesions arise.
Carcinomas are a type of cancer that develops from epithelial cells. Specifically, a carcinoma is a cancer that begins in a tissue that lines the inner or outer surfaces of the body, and that generally arises from cells originating in the endodermal or ectodermal germ layer during embryogenesis. The term carcinoma has also come to encompass malignant tumors composed of transformed cells whose origin or developmental lineage is unknown (see cancer of unknown primary origin (CUP)), but that possess certain specific molecular, cellular, and histological characteristics typical of epithelial cells. This may include the production of one or more forms of cytokeratin or other intermediate filaments, intercellular bridge structures, keratin pearls, and/or tissue architectural motifs such as stratification or pseudo-stratification. Common malignancies, such as breast, colon, and lung cancer, are almost always carcinoma. Other types of carcinomas include squamous-cell carcinomas (oral cancers), lung cancers, breast (ductal) carcinoma, prostate (adenocarcinoma), colon and rectum (adenocarcinoma or squamous cell carcinoma), pancreatic (adenocarcinoma), ovarian, hepatocellular and renal cell carcinoma.
A sarcoma is a cancer that arises from transformed cells of mesenchymal origin. Thus, malignant tumors made of cancellous bone, cartilage, fat, muscle, vascular, or hematopoietic tissues are, by definition, considered sarcomas. Sarcomas occur much less frequently in humans than carcinomas. Types of sarcomas include, for example, osteosarcoma, chondrosarcoma, liposarcoma, and leiomyosarcoma.
Lymphoma refers to cancers that originate in the lymphatic system. Lymphoma is characterized by malignant neoplasms of lymphocytes—B lymphocytes and T lymphocytes (i.e., B-cells and T-cells). Lymphoma generally starts in lymph nodes or collections of lymphatic tissue in organs including, but not limited to, the stomach or intestines. Lymphoma may involve the marrow and the blood in some cases. Lymphoma may spread from one site to other parts of the body.
Such lymphomas include, but are not limited to, Hodgkin's lymphoma, non-Hodgkin's lymphoma, cutaneous B-cell lymphoma, activated B-cell lymphoma, diffuse large B-cell lymphoma (DLBCL), mantle cell lymphoma (MCL), follicular center lymphoma, transformed lymphoma, lymphocytic lymphoma of intermediate differentiation, intermediate lymphocytic lymphoma (ILL), diffuse poorly differentiated lymphocytic lymphoma (PDL), centrocytic lymphoma, diffuse small-cleaved cell lymphoma (DSCCL), peripheral T-cell lymphomas (PTCL), cutaneous T-Cell lymphoma and mantle zone lymphoma and low grade follicular lymphoma.
Non-Hodgkin's lymphoma (NHL) is the fifth most common cancer for both men and women in the United States, with an estimated 63,190 new cases and 18,660 deaths in 2007. Jemal A, et al., CA Cancer J Clin 2007; 57(1):43-66. The probability of developing NHL increases with age and the incidence of NHL in the elderly has been steadily increasing in the past decade, causing concern with the aging trend of the US population. Id. Clarke C A, et al., Cancer 2002; 94(7):2015-2023.
Diffuse large B-cell lymphoma (DLBCL) accounts for approximately one third of non-Hodgkin's lymphomas. While some DLBCL patients are cured with traditional chemotherapy, the remainder die from the disease. Anticancer drugs cause rapid and persistent depletion of lymphocytes, possibly by direct apoptosis induction in mature T and B cells. See K. Stahnke. et al., Blood 2001, 98:3066-3073. Absolute lymphocyte count (ALC) has been shown to be a prognostic factor in follicular non Hodgkin's lymphoma and recent results have suggested that ALC at diagnosis is an important prognostic factor in diffuse large B-cell lymphoma. See D. Kim et al., Journal of Clinical Oncology, 2007 ASCO Annual Meeting Proceedings Part I. Vol 25, No. 18S (June 20 Supplement), 2007: 8082.
Hematological Cancers
Leukemia refers to malignant neoplasms of the blood-forming tissues. Various forms of leukemias are described, for example, in U.S. Pat. No. 7,393,862 and U.S. provisional patent application No. 60/380,842, filed May 17, 2002, the entireties of which are incorporated herein by reference. Although viruses reportedly cause several forms of leukemia in animals, causes of leukemia in humans are to a large extent unknown. The Merck Manual, 944-952 (17th ed. 1999). Transformation to malignancy typically occurs in a single cell through two or more steps with subsequent proliferation and clonal expansion. In some leukemias, specific chromosomal translocations have been identified with consistent leukemic cell morphology and special clinical features (e.g., translocations of 9 and 22 in chronic myelocytic leukemia, and of 15 and 17 in acute promyelocytic leukemia). Acute leukemias are predominantly undifferentiated cell populations and chronic leukemias more mature cell forms.
Acute leukemias are divided into lymphoblastic (ALL) and non-lymphoblastic (ANLL) types. The Merck Manual, 946-949 (17th ed. 1999). They may be further subdivided by their morphologic and cytochemical appearance according to the French-American-British (FAB) classification or according to their type and degree of differentiation. The use of specific B- and T-cell and myeloid-antigen monoclonal antibodies are most helpful for classification. ALL is predominantly a childhood disease which is established by laboratory findings and bone marrow examination. ANLL, also known as acute myelogenous leukemia or acute myeloblastic leukemia (AML), occurs at all ages and is the more common acute leukemia among adults; it is the form usually associated with irradiation as a causative agent.
Chronic leukemias are described as being lymphocytic (CLL) or myelocytic (CML). The Merck Manual, 949-952 (17th ed. 1999). CLL is characterized by the appearance of mature lymphocytes in blood, bone marrow, and lymphoid organs. The hallmark of CLL is sustained, absolute lymphocytosis (>5,000/μL) and an increase of lymphocytes in the bone marrow. Most CLL patients also have clonal expansion of lymphocytes with B-cell characteristics. CLL is a disease of middle or old age. In CML, the characteristic feature is the predominance of granulocytic cells of all stages of differentiation in blood, bone marrow, liver, spleen, and other organs. In the symptomatic patient at diagnosis, the total white blood cell (WBC) count is usually about 200,000/μL, but may reach 1,000,000/μL. CML is relatively easy to diagnose because of the presence of the Philadelphia chromosome.
In addition to the acute and chronic categorization, neoplasms are also categorized based upon the cells giving rise to such disorder into precursor or peripheral. Precursor neoplasms include ALLs and lymphoblastic lymphomas and occur in lymphocytes before they have differentiated into either a T- or B cell. Peripheral neoplasms are those that occur in lymphocytes that have differentiated into either T- or B-cells. Such peripheral neoplasms include, but are not limited to, B-cell CLL, B-cell prolymphocytic leukemia, lymphoplasmacytic lymphoma, mantle cell lymphoma, follicular lymphoma, extranodal marginal zone B-cell lymphoma of mucosa associated lymphoid tissue, nodal marginal zone lymphoma, splenic marginal zone lymphoma, hairy cell leukemia, plasmacytoma, diffuse large B-cell lymphoma and Burkitt lymphoma. In over 95 percent of CLL cases, the clonal expansion is of a B cell lineage. See Cancer: Principles & Practice of Oncology (3rd Edition) (1989) (pp. 1843 1847). In less than 5 percent of CLL cases, the tumor cells have a T-cell phenotype. Notwithstanding these classifications, however, the pathological impairment of normal hematopoiesis is the hallmark of all leukemias.
Multiple myeloma (MM) is a cancer of plasma cells in the bone marrow. Normally, plasma cells produce antibodies and play a key role in immune function. However, uncontrolled growth of these cells leads to bone pain and fractures, anemia, infections, and other complications. Multiple myeloma is the second most common hematological malignancy, although the exact causes of multiple myeloma remain unknown. Multiple myeloma causes high levels of proteins in the blood, urine, and organs, including but not limited to M-protein and other immunoglobulins (antibodies), albumin, and beta-2-microglobulin. M-protein, short for monoclonal protein, also known as paraprotein, is a particularly abnormal protein produced by the myeloma plasma cells and can be found in the blood or urine of almost all patients with multiple myeloma.
The incidence of cancer continues to climb as the general population ages, as new cancers develop, and as susceptible populations grow. A tremendous demand therefore exists for new methods, treatments and compositions that can be used to treat patients with cancer.
The role of mitogen-activated protein kinase (MAPK), such as MAPK1/2 (ERK1/2), signaling in the development of cancer has been studied extensively. The “MAPK pathway,” or the RAS-RAF-MEK-MAPK/ERK pathway, involves signaling and phosphorylation that plays a key role in regulation of cell growth differentiation, proliferation, apoptosis and migration functions. MAPKs play an important role in the transmission of extracellular signals into intracellular responses. Activation of MAPK results from a three-kinase cascade consisting of a MAPK kinase kinase (MAPK3)(e.g., Raf, MLK, TAK) which phosphorylates and activates a MAPK kinase (e.g., MEK), which then phosphorylates and increases the activity of one or more MAPKs (e.g., ERK1/2). MAPK3s are regulated by growth factor dependent Ras proteins. Activated MAPKs phosphorylate various intracellular targets. Dhillon, et al., 2007, Oncogene, vol. 26, 3279-3290.
Dysregulation or abnormal activation of the MAPK pathway has been implicated in human cancers. Therefore, inhibitors targeting the MAPK pathway have been the subject of intense study in recent years. Santarpia, et al., 2012, Expert Opin. Ther. Targets, vol. 16(1), 103-119); Zaganj or, et al., 2011, Tocris Reviews, no. 35 (available at http://www.komabiotech.co.kr/pdf/mapk_signaling_review.pdf).
It has also been shown that mutations in genes encoding receptors (e.g., EGFR) and signal transducers (e.g., RAS) upstream of MAPK, as well as downstream kinases (e.g., BRAF) are implicated in human cancers. Burotto, et al., 2014, Cancer, 3446-3456. Thus, the MAPK pathway presents a logical target for anticancer drug development.
Methods of Treating Cancer
Current cancer therapy may involve surgery, chemotherapy, hormonal therapy and/or radiation treatment to eradicate neoplastic cells in a patient (see, for example, Stockdale, 1998, Medicine, vol. 3, Rubenstein and Federman, eds., Chapter 12, Section IV). Recently, cancer therapy could also involve biological therapy or immunotherapy. All of these approaches may pose significant drawbacks for the patient. Surgery, for example, may be contraindicated due to the health of a patient or may be unacceptable to the patient. Additionally, surgery may not completely remove neoplastic tissue. Radiation therapy is only effective when the neoplastic tissue exhibits a higher sensitivity to radiation than normal tissue. Radiation therapy can also often elicit serious side effects. Hormonal therapy is rarely given as a single agent. Although hormonal therapy can be effective, it is often used to prevent or delay recurrence of cancer after other treatments have removed the majority of cancer cells. Certain biological and other therapies are limited in number and may produce side effects such as rashes or swellings, flu-like symptoms, including fever, chills and fatigue, digestive tract problems or allergic reactions.
With respect to chemotherapy, there are a variety of chemotherapeutic agents available for treatment of cancer. A number of cancer chemotherapeutics act by inhibiting DNA synthesis, either directly or indirectly by inhibiting the biosynthesis of deoxyribonucleotide triphosphate precursors, to prevent DNA replication and concomitant cell division. Gilman et al., Goodman and Gilman's: The Pharmacological Basis of Therapeutics, Tenth Ed. (McGraw Hill, New York).
Despite availability of a variety of chemotherapeutic agents, chemotherapy has many drawbacks. Stockdale, Medicine, vol. 3, Rubenstein and Federman, eds., ch. 12, sect. 10, 1998. Almost all chemotherapeutic agents are toxic, and chemotherapy causes significant and often dangerous side effects including severe nausea, bone marrow depression, and immunosuppression. While targeted therapy with chemotherapeutic agents, in particular small molecules, may address some of these issues, they are not a panacea and do not resolve all such issues. See, e.g., http://www.cancer.org/treatment/treatmentsandsideeffects/treatmenttypes/targetedtherapy/targeted-therapy-toc. Additionally, even with administration of combinations of chemotherapeutic agents, many tumor cells are resistant or develop resistance to the chemotherapeutic agents. In fact, those cells resistant to the particular chemotherapeutic agents used in the treatment protocol often prove to be resistant to other drugs, even if those agents act by different mechanism from those of the drugs used in the specific treatment. This phenomenon is referred to as multidrug resistance. Because of the drug resistance, many cancers prove refractory to standard chemotherapeutic treatment protocols.
Thus, there exists a significant need for compounds, compositions and methods for treating, preventing and managing cancer.
Inflammatory Disease
In addition to ERK1/2, the MAPKs ERK5, c-Jun N-terminal kinases (JNKs) and p38 isoforms (p38α, p38β, p38γ and p38δ) have been shown to be implicated in inflammatory response. Huang, et al. 2010, Protein Cell, 1(3), 218-226. MAPKs have been shown to play important roles in embryonic development and adult tissue homeostasis, and in particular chronic inflammation and inflammation-associated cancer development.
JNKs (also referred to as stress-activated kinases (SAPKs)) are activated by a MAPK3 cascade via MEK4 and MEK7. Manzoor, et al., 2012, J. Bacter. Virology, vol. 42(3), 189-195. JNKs regulate cell proliferation and apoptosis by activating various targets, including the AP-1 transcript factors. AP-1s are activated by, e.g., cytokines, stress, growth factors and infections, and are invoved in managing proliferation, differentiation and apoptosis.
Therefore, compounds that inhibit MAPKs are expected to be effective in treatment of inflammatory conditions.